JPH0126872B2 - - Google Patents

Description

[Detailed description of the invention]

Technical Field The present invention relates to a battery-powered thermal printer that prints using a thermal head in which a large number of heating elements are arranged, and in particular to an improvement in the excitation method of a step motor that reciprocates the thermal head along a platen. It is related to. Prior Art A thermal printer prints by pressing a thermal head against printing paper and moving it along a platen to generate heat from a number of heating elements arranged in the thermal head. When the thermal head of a printer is moved more than a certain amount without printing,
Conventionally, it has been done to release the pressure of the thermal head against the printing paper. Further, a step motor has been conventionally used as a drive motor for reciprocating the thermal head along the platen. However, conventionally, both when moving the thermal head in a state where it is pressed against the printing paper (hereinafter referred to as the crimped state), and when moving the thermal head when the pressure on the printing paper is released (hereinafter referred to as the released state), Both step motors were driven using the same excitation method. Since the load when moving a thermal head in a dissociated state is smaller than the load when moving a thermal head in a crimped state,
Although the driving force of the step motor can be small, conventionally the step motors were excited using the same excitation method so that they could generate the same driving force, so the moving speed of the thermal head in the dissociated state was However, the battery life was short and limited. Purpose of the Invention The present invention was made based on the discovery of this fact, and it is possible to change the excitation method of the step motor depending on whether the thermal head is being moved in a crimped state or when it is being moved in a dissociated state. Therefore, it is an object of the present invention to provide a thermal printer that can move a dissociated thermal head at a higher speed than conventional printers and can extend battery life. Structure of the Invention In order to achieve the above object, the present invention includes (a) a thermal head in which a large number of heating elements are arranged, (b) a platen that supports printing paper, and (c) a thermal head arranged along the platen. A drive motor that drives the motor back and forth;
(d) When printing, press the thermal head against the printing paper,
In a battery-powered thermal printer, the drive motor is replaced by a step motor in a battery-driven thermal printer having a head pressure release means for releasing the pressure of the thermal head against the printing paper when the thermal head is moved beyond a predetermined amount without printing. The excitation method of the step motor is 2-phase excitation during printing, and 1-phase excitation is used when the thermal head is moved from the press release state to the printing paper.
- An excitation method switching means for switching to two-phase excitation is provided. Effects of the Invention For example, when operating four-phase step motors at the same speed, the power consumption for 1-2 phase excitation is approximately three-quarters of the power consumption for 2-phase excitation, and it is Even when moving, the power consumption is lower than when two-phase excitation is performed, and the life of the battery is extended accordingly. When operating a 4-phase step motor at the same speed with 1-2 phase excitation and 2-phase excitation, current is supplied to the step motor according to the time charts shown in the upper and lower parts of Figure 5, respectively. However, in this case, one cycle of two-phase excitation is AB,
B,,A, and one cycle of 1-2 phase excitation is AB,B,B,,,A,A
In order to operate the step motor at the same speed using both excitation methods, it is necessary to complete each cycle at the same time. In this case, as is clear from Fig. 5, in two-phase excitation, the total time during which current is supplied to the four phases A, B, A, and A is 8 units of time (1 unit of time is In Fig. 5, the time corresponds to the interval between adjacent thin vertical lines), whereas
In 1-2 phase excitation, it is 6 units of time and 1
- The power consumption of two-phase excitation is about three-quarters of the power consumption of two-phase excitation. Of course, in a normal step motor, when 1-2 phase excitation is used, the driving force that can be generated is lower than when 2-phase excitation is used, but the load when moving the head in the disengaged state is also small. Therefore, the head is 1
-It can be moved without any problem with two-phase excitation. Furthermore, since the amount of current that can be obtained from a battery in a certain period of time is limited, the amount of work that can be performed in a certain period of time is also limited. However, as mentioned above, the load when moving a thermal head in a dissociated state is smaller than that when moving a thermal head in a crimped state, so if the amount of work performed in a given time is the same in both cases, When the thermal head is in the disengaged state, it is possible to move the thermal head at a higher speed than when it is in the compressed state. Therefore, it is possible to increase the speed when moving the carriage over long distances, such as when performing line feeds, and the efficiency of printing operations can be improved. In addition, it is inevitable for batteries to gradually drop in voltage as they are used, and when a large amount of power is consumed, it is unavoidable that the voltage will drop temporarily. If the voltage falls below a certain level, the step motor will lose synchronization, and this will determine the battery life. Therefore, when it is necessary to move the thermal head at high speed, such as during line feed, temporary voltage drops can be avoided by driving the step motor with 1-2 phase excitation, which essentially consumes less power. This makes it possible to set a high movement speed of the thermal head and still obtain a long battery life. Additionally, some step motors, such as high-speed permanent magnet motors, have characteristics that allow them to obtain almost the same driving force with 1-2 phase excitation as with 2-phase excitation at the same voltage and speed. However, when such a step motor is driven by batteries, it is possible to rotate it at a higher speed with 1-2 phase excitation than with 2-phase excitation, taking into consideration the temporary voltage drop mentioned above. The moving speed of the thermal head at the time of line feed etc. can be set high, printing efficiency is improved and power consumption is further reduced. Embodiment Hereinafter, an embodiment of the present invention will be described in detail based on the drawings. FIG. 1 is a diagram showing the external appearance of a typewriter that is an embodiment of the present invention. As is clear from this diagram, a keyboard 10 is provided at the front of the typewriter, and a printing mechanism is located at the rear. 11 are provided. The keyboard 10 has various keys arranged thereon, and is also provided with a liquid crystal display 12 capable of displaying a certain number of key input data. Also,
The printing mechanism section 11 includes a platen 14 in the form of a longitudinal plate,
Carriage 1 moving along its platen 14
6, a thermal head 18 supported by the carriage 16 is provided. This typewriter is powered by dry batteries, and
It is small and lightweight, making it portable. FIG. 2 shows an enlarged view of the printing mechanism section 11.
The carriage 16 is supported by a guide rod 20 having a circular cross section and a guide plate 22 having a longitudinal plate shape, which are arranged parallel to the platen 14.
It is movable along the platen 14. The carriage 16 is reciprocated by a four-phase step motor 28 via a timing belt 24 and a timing pulley 26. A head carriage 30 is further supported on the guide rod 20 so as to be relatively rotatable, and is sandwiched between two arms 32 (only one of which is shown) provided on the carriage 16 at a constant interval. Although it moves integrally with the carriage 16 in the longitudinal direction, it can rotate around the guide rod 20 independently of the carriage 16. A thermal head 18 in which a large number of heating elements are arranged is fixed to this head carriage 30 (more precisely, what is shown in FIG. 2 is the head carriage 30).
The thermal head 18 is fixed to the surface of the heat sink that faces the platen 14). The head carriage 30 further includes an arm (not shown) extending radially outwardly of the guide rod 20, below the carriage 16, and generally parallel to the carriage 16, with a longitudinal arm extending parallel to the platen 14 below the arm. A shaped drive plate 33 is provided, and a pair of arms provided at both ends of the drive plate 33 are rotatably supported by the guide rod 20. And this drive plate 3
The tongue protruding from one end of 3 is a bell crank 34.
can be engaged with one arm of the The bell crank 34 is rotatably supported by a short shaft 36 fixed to the main frame 38, and the arm on the opposite side of the bell crank 34 from the side that engages with the drive plate 33 is connected to the output rod of the solenoid 40. 42. Since the head carriage 30 and the bell crank 34 are each urged by a spring (not shown) to rotate clockwise in FIG. 2, the thermal head 18 is always in a disengaged state away from the platen 14. However, when current is supplied to the solenoid 40, the solenoid 40 is pressed against the platen 14 via the bell crank 34 and the drive plate 33 against the biasing force of the spring, and the head carriage 30, The drive plate 33, bell crank 34, solenoid 40, spring, etc. constitute a head press-release means. A paper guide 44 for guiding the printing paper is disposed at the rear of the platen 14, and the printing paper guided by this paper guide 44 and inserted is sandwiched between a pair of paper feed rollers 46 and 48 and transferred to the platen. 14 and the thermal head 18. 50 is paper feed roller 4
It is a step motor for driving 6, and 52
is a release lever for moving the paper feed rollers 46, 48 to non-operating positions separated from each other. The typewriter having the above structure is controlled by a control circuit shown in FIG. As is clear from the figure, the keyboard 10 is connected to a CPU (central processing unit) 60, which
A ROM (read only memory) 62 and a RAM (random access memory) 64 are connected to the memory 60 . The ROM 62 stores programs for controlling the operation of the typewriter, including the program shown in the flowchart in FIG. The thermal head 18 is moved along the platen 14, including an input buffer memory 66 for storing, a text memory 68 capable of storing print data of a document of 3 to 4 pages, and a print buffer memory 70 for temporarily storing data to be printed. Movement amount register 7 that stores the movement amount of the carriage 16 necessary for moving the carriage 16
2. Various registers are provided, including a high speed flag register 74 that stores a high speed flag indicating that the carriage 16 should be moved at high speed, and a rotation direction register 76 that stores the rotation direction of the step motor 28. The CPU 60 further includes a head crimping and releasing circuit 80,
A thermal head drive circuit 82, a carriage drive circuit 84 and a display controller 85 are connected. The head crimping and releasing drive circuit 80 energizes the solenoid 40 to press the thermal head 18 to the platen 14, and demagnetizes the thermal head 18 to separate it from the platen 14. Based on the pattern data read from the ROM 62 by the CPU 60 based on the code data stored in the buffer memory 70, the thermal head 18
A predetermined one of the plurality of heating elements is made to generate heat. The carriage drive circuit 84 controls the rotation of the step motor 28 that drives the carriage 16 to move the thermal head 18 along the platen 14.
is configured so that it can be excited by both a 1-2 phase excitation method and a 2-phase excitation method. Further, the display controller 85 causes the liquid crystal display 12 to display data inputted by keys. The typewriter of this embodiment configured as described above has a direct print mode in which printing is performed simultaneously with key input from the keyboard 10, and a direct print mode in which printing is performed simultaneously with key input from the keyboard 10, by switching the mode selection switch provided on the keyboard 10. While the data is being displayed on the LCD display 12, printing will not be performed.
A collection print mode in which typos are corrected and the data that overflows from the liquid crystal display 12 is printed in order, and a non-print mode in which key-input data is exclusively stored in the text memory 68 without printing. However, since the operation itself in each mode is not necessary for understanding the present invention, a detailed explanation will be omitted. Taking as an example a case in which stored data is printed all at once after storage, only the portions that are closely related to the present invention will be explained based on the flowchart shown in FIG. The data stored in the text memory 68
The data is sequentially read out by the CPU 60, and based on the read data, a head pressure/release drive circuit 80, a thermal head drive circuit 82, a carriage drive circuit 84, and a paper feed drive circuit (not shown) are controlled to perform printing. However, in this case,
Carriage drive circuit 84 is controlled according to a program shown in the flowchart of FIG. First, in step S1, the text memory 6
The data read from 8 is sent to the step motor 28 as a print command, line feed command, tab operation command, etc.
A determination is made as to whether or not the data is a command that involves rotation, and if the determination result is YES, step S2
At step 3, it is determined whether the data is print command data or not. If the result of the determination is YES, step S3 is executed and a predetermined movement amount for one character is stored in the movement amount register 72. Also, the result of the judgment in step S2 is
If NO, that is, if the data is a line feed command or a tab operation command, step S4
The amount of movement of the thermal head 18 necessary to execute the command is calculated, and the calculation result is stored in the movement amount register 72. It is determined in step S5 whether the head movement amount set in step S4 is larger than a predetermined reference amount, and if it is larger than the reference amount, a high speed flag is set in step S6. That is, the contents of the high-speed flag register 74 are set to [1]. On the other hand, if the movement amount is smaller than the reference amount, the high speed flag is reset in step S7, that is, the contents of the high speed flag register 74 are

It is set to [0]. Of course, since the amount of movement for one character set in step S3 is smaller than the reference amount of movement, the high speed flag is reset in this case as well. Next, in step S8, step motor 2
8 rotation directions are set. That is, this typewriter is capable of printing in both forward and reverse directions, and the printing direction is determined so that the amount of movement of the thermal head 18 at the time of line feed is minimized. The rotation direction determined in this way is stored in the rotation direction register 76. Next, in step S9, it is determined whether the high speed flag is set or not.
If not set, that is, if the amount of movement of the head is small, step S10 is executed, and the excitation method of the step motor 28 is switched to two-phase excitation. On the other hand, if the moving amount of the head is larger than the reference amount and the high speed flag is set, step S11 is executed and the excitation method of the step motor 28 is switched to 1-2 phase excitation. That is,
A selection is made between two-phase excitation data as shown in Table 1 and 1-2 phase excitation data as shown in Table 2, which are stored in the ROM 62. Note that the rotational direction of the step motor 28 is reversed by reversing the reading direction of each data.

【table】

【table】

[Table] Once the above switching is complete, step S12
In step S13, the step motor 28 is excited with an excitation phase corresponding to the two-phase excitation method or the 1-2 phase excitation method, and the excitation state is maintained for a pulse width corresponding to the two-phase excitation method or the 1-2 phase excitation method in step S13. The excitation state is terminated in step S14. The pulse width for each excitation method is determined in advance so that the step motor 28 rotates at a higher speed when 1-2 phase excitation is used than when 2 phase excitation is used, and the excitation state is changed by the pulse width. is maintained. and,
In step S15, it is determined whether or not the head has been moved by the amount of movement set in the movement amount register 72 in step S3 or S4. If the head has not been moved, the program execution returns to step S9, and from then on, the step motor is moved. 28 is sequentially excited and rotated with different excitation phases. If the thermal head 18 has been moved by the amount stored in the movement amount register 72, the program execution returns to the start. As is clear from the above description, in the typewriter of this embodiment, movement of the thermal head 18 accompanied by printing and movement over a relatively short distance are performed by two-phase excitation of the step motor 28, and the comparison of the thermal head 18 is Movement over long distances is performed by 1-2 phase excitation, and switching of the excitation method is automatically performed based on print data. The above explanation has been made regarding the case where the data stored in the text memory 68 is sequentially read out and printed. However, when the typewriter of this embodiment is used in the direct print mode or the collection print mode, too,
If the moving distance of the thermal head 18 is long when line feed data, tab operation data, etc. are input by key, the excitation method of the step motor 28 is switched. The above has described in detail an embodiment in which the present invention is applied to a typewriter belonging to a printer in the broad sense. The present invention can also be applied to a thermal printer that is equipped with a thermal head and is powered by a battery, and can also be applied to a thermal printer that prints in only one direction. It is. In addition, although not illustrated in detail, the present invention may be carried out in a manner in which various modifications and improvements are made to the configuration of the printing mechanism section, the control circuit, the program for switching the excitation method of the step motor, etc. based on the knowledge of those skilled in the art. Of course it is possible.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the appearance of a typewriter equipped with a thermal head according to an embodiment of the present invention, and FIG. 2 is a perspective view showing only the printing mechanism of the typewriter. FIG. 3 is a block diagram of a control circuit that controls the operation of the typewriter, and FIG. 4 is a flowchart showing only the portions of the program stored in the ROM of the control circuit that are closely related to the present invention. It is. FIG. 5 is a time chart for explaining why power consumption can be saved by the present invention. 10: Keyboard, 14: Platen, 16: Carriage, 18: Thermal head, 28: Step motor (drive motor), 33: Drive plate, head pressure release means, 34: Bell crank, head pressure release means, 36: Short shaft , head crimping and releasing means, 4
0: Solenoid, head pressure release means, 60:
CPU (central processing unit) (excitation method switching means) 62:
ROM (read only memory) (excitation method switching means), 64: RAM (random access memory)
(Excitation method switching means) 80: Head crimping and releasing drive circuit (excitation method switching means).

Claims (1)

[Scope of Claims] 1. A thermal head in which a large number of heating elements are arranged, a platen that supports printing paper, a drive motor that drives the thermal head back and forth along the platen, and a thermal head that drives the thermal head back and forth along the platen; A battery-driven thermal printer having head pressure release means that presses the thermal head and releases the pressure of the thermal head against the printing paper when the thermal head is moved by more than a predetermined amount without printing, The drive motor is constituted by a step motor, and the excitation method of the step motor is two-phase excitation during printing, and 1-2 phase excitation is used when the thermal head is moved from the press release state to the printing paper.
A thermal printer characterized by having an excitation method switching means for switching to phase excitation.